The precise mechanisms by which aldosterone (Aldo) and other mineralocorticoid hormones modulate sodium transport are unknown. It is now clear that Aldo induces the synthesis of mRNA and proteins in target tissues. This Aldo-induced synthesis offers an opportunity to radioactively label the key elements in the physiologic response to Aldo. We will isolate and characterize the labeled Aldo-induced proteins with regard to: 1) ionophoric properties, 2) ouabain binding, 3) amiloride binding, and 4) ATPase activity. Aldo-induced mRNA will also be used as a tool to study Aldo-induced translation products. These studies will be correlated with the radioactive labeling of Aldo-responsive proteins in the apical membrane.